Percutaneous transluminal angioplasty is a method that has been practiced widely, for example, for treatment of stricture site or obstruction site of vascular lumen by dilation and for recovery or improvement of blood flow in coronary arteries and peripheral blood vessels. The balloon catheter used in the percutaneous transluminal angioplasty has a shaft and a balloon inflatable and deflatable freely by regulation of its inner pressure that is connected to the terminal region of the shaft, and the shaft generally has a structure in which a lumen for inserting a guide wire (guide wire lumen) and a lumen for supplying a pressurized fluid for regulation of the balloon inner pressure (inflation lumen) are formed in the shaft in the length direction.
The percutaneous transluminal coronary angioplasty (PTCA) by using such a balloon catheter is generally practiced as follows: First, a guide catheter is inserted from a puncture site such as femoral artery, brachial artery, or radial artery, while the distal end is fed via aorta into the entrance of coronary artery. Then, a guide wire inserted in the guide wire lumen is fed beyond the stricture site of coronary artery, and a balloon catheter is then inserted along the guide wire, while the balloon is delivered to the stricture site. Then, the stricture site is dilated and treated by dilation of the balloon by supply of a pressurized fluid via the inflation lumen using a device such as indeflator. After completion of the treatment of the stricture site by dilation, the PTCA is completed by deflating the balloon under reduced pressure and withdrawing it out of the body.
Each catheter described above has a structure in which a distal shaft and a proximal shaft are connected to each other and an adaptor member holding the catheter is connected to the proximal end of the proximal shaft, and such catheters are divided roughly into two groups, depending on the length of the guide wire lumen. Hereinafter, balloon catheters having a balloon connected to the distal side of the distal shaft and a port for supplying a pressurized fluid for regulation of the inner pressure of the balloon to the inflation lumen will be described as examples.
One is an over-the-wire catheter (OTW catheter) having a guide wire lumen formed over the entire length of a catheter as shown in FIG. 1, wherein a proximal end-sided opening of guide wire lumen and an opening of inflation lumen are formed in adaptor member, a strain relief for control of flexibility in the axial direction is also formed on the adaptor member, and a distal end-sided opening of the guide wire lumen is formed in the most distal end region of balloon or to the distal side of the most distal end region of balloon. Another example thereof is a rapid exchange catheter (RX catheter) shown in FIG. 2, in which a guide wire lumen is present only on the distal side of balloon catheter and a proximal end-sided opening of the guide wire lumen is formed in the middle of the distal shaft.
Since the OTW catheter has a guide wire lumen over the entire length of the balloon catheter, it is often used for sending a guide wire to the lesion that prohibits passage of the guide wire, but the operation of withdrawing the balloon catheter while leaving the guide wire in the lesion area is rather complicated and causes problems. Thus, the OTW catheter demands additional special device and operation such as insertion of an exchange extension wire for withdrawal of the balloon catheter while the guide wire is left in the lesion.
On the other hand, the guide wire lumen is present only on the distal side of the balloon catheter in the RX catheter; thus, the convenience of operation is very favorable, as it is possible to remove, exchange, reinsert the balloon catheter easily while leaving the guide wire in the lesion area; and it is also possible to shorten the surgical period and reduce the number of devices used.
Catheters are roughly divided into two groups, depending on the shaft structure of the region having the guide wire lumen. One is a coaxial catheter, as shown by the crosssectional shape in the FIG. 4, having an inner shaft and an outer shaft coaxially surrounding the inner shaft, forming a guide wire lumen by the lumen of the inner shaft and an inflation lumen having a circular crosssectional shape between the inner shaft and the outer shaft. The other is a biaxial catheter wherein the guide wire lumen and the second lumen are arranged in parallel with each other.
In the case of an OTW catheter, the catheter generally has a coaxial or biaxial structure over the entire length. Alternatively in the case of an RX catheter, the distal shaft in the region having the guide wire lumen may have a coaxial or biaxial structure.
Various methods are disclosed for improving the convenience of operating of such catheter.
Patent Document 1 discloses a balloon catheter and a balloon having an ionic deposition film harder than the base material, formed on the surface of its stripe- or film-shaped soft resin base material.
According to the prior art, the balloon catheter and the balloon described above, if they carry an ionic deposition film formed, become flexible to a bending force, but more rigid to the force in the direction parallel to the surface, and resistant for example to buckling when the catheter is compressed. However, presence of the ionic deposition film was not effective in the insertion operation, because the film was highly vulnerable to cracking, ionically deposited substances may be released into the blood vessel, possibly showing adverse effects on the body, and the energy irradiation during ionic deposition may harden the balloon region, making it difficult to reinsert the catheter after dilation of balloon to the same or another stricture site (recross).
Patent Document 2 discloses a balloon catheter in a double-lumen structure consisting of an inner shaft and an outer shaft allowing penetration of the guide wire in the region of the catheter close to the terminal region, wherein a guide tube having an inner diameter smaller than the inner diameter of the outer shaft and larger than the outer diameter of the inner shaft is placed at least in the terminal region of the outer shaft.
According to the prior art, it is possible by installing the guide tube described above to improve the rewrap efficiency of the balloon after dilation while preventing loosening of the inner shaft, by relaxing the discontinuity in rigidity in the junction region between the outer shaft and the balloon and thus, preventing folding, to improve the insertion efficiency of the catheter in the blood vessel and the traveling efficiency thereof in the stricture site, to prevent the accordion phenomenon, and to improve the pressurization efficiency. However, installation of a guide tube on part of the inner shaft leads to generation of discontinuous change in rigidity in the region close to the guide tube and expansion of the outer diameter, increasing the wrapping size of the balloon, and thus, there are still many problems to be overcome.
Patent Document 3 discloses an OTW catheter having a first tubular part forming a guide wire lumen, a second tubular part extending in the same direction with the first tubular and having the outer face bound to the peripheral surface of the first tubular part, forming an dilation lumen, and a means of changing the flexibility of at least one of the balloon and the first and second tubular parts.
According to the prior art, in the case of a catheter having biaxial shafts described above, it is possible to select the properties of the catheter properly and thus to obtain a catheter with favorable properties, by selecting the respective components for the catheter having the first and second tubular parts and the part controlling flexibility. It is also possible to reduce cost, because the production method is simpler. However, such a catheter demands an adhesive or sleeve parts for connection of the first and second tubular parts, which leads to increase in the diameter and decrease of the flexibility of the connecting region, and thus, was not sufficiently favorable in the convenience of inserting the catheter into bent blood vessel.
Patent Document 4 discloses a long and thin catheter having an inner tubular part, an outer tubular part, and an inflatable balloon, wherein there is a second lumen formed between the inner and outer tubular parts, the inflatable balloon communicates with the second lumen, the catheter has an bonded longitudinal region for bonded between the inner and outer tubular parts, the bonded longitudinal region occupies at least 30% of the inner surface of the outer tubular part, and the inner circumference face of the catheter is bonded to the outer face of the inner tubular part.
According to the prior art, by bonding a length of the outer tubular member to the exterior of the inner member, the profile of the catheter body in at least one transverse dimension in that area is reduced and thus to reduce the diameter in the region. In addition, mutual support between the inner and outer tubular parts in the bonded longitudinal region improves the pressure transmission efficiency of the catheter. However, the bonded longitudinal region, where the inner and outer tubular parts are bonded to each other, is lower in flexibility, and thus, it was difficult to send the catheter by pushing the bonded longitudinal region through a bent blood vessel. The catheter also had a problem that the second lumen in the bonded longitudinal region was vulnerable to deformation when the bonded longitudinal region was bent, and the inflation/deflation response of the inflatable balloon was lower.
Patent Document 5 discloses a long and thin catheter having a balloon, i.e., a coaxial balloon dilation catheter, wherein the shaft of the catheter consists of an inner tube and an outer tube surrounding the inner tube, there is an inflation/deflation lumen formed between them, the inner tube is connected to the outer tube at the position distal from the proximal end region of the shaft.
In a catheter having a shaft of coaxial tubes and a balloon connected to the distal end region of the tubes, the coaxial tubes are likely to be deformed into the nested pattern when an increased resistance is applied. The balloon deforms into an accordion-like shape by deformation in a nested pattern, making the balloon more resistant to passage through a stricture site. According to the prior art, the pressure transmission efficiency of catheter is increased by connection of the distal end region of the outer tube to the inner tube. The length of the balloon in the axial direction is kept constant for prevention of the deformation of the tube into the nested pattern. It is thus possible to prevent accordion-like deformation of the balloon and retain its favorable balloon-inserting efficiency in the stricture site. However, also in the prior art, the region where the outer and inner tubes are connected is lower in flexibility, lowering the efficiency of passing the region through a bent blood vessel. In addition when the position is bent, the inflation/deflation lumen in the region deforms more easily, undesirably lowering the inflation/deflation response of the balloon.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 9-111021
Patent Document 2: WO99/17831
Patent Document 3: Japanese Unexamined Patent Application Publication No. 7-132147
Patent Document 4: Japanese Unexamined Patent Application Publication No. 5-137793
Patent Document 5: Japanese Unexamined Patent Application Publication No. 3-51059